Implantable Medical Device for Stimulating a Human or Animal Heart

ABSTRACT

An implantable medical device for stimulating a heart, comprising a control unit, a memory unit, a stimulation unit for stimulating a cardiac region of a heart, and a detection unit for detecting an electrical signal of the heart. The memory unit comprises a computer-readable program that causes the control unit to perform the following steps: a) detecting capture thresholds during an observation period, each capture threshold detected in response to a sequence of pacing pulses delivered by the stimulation unit; b) storing the detected capture thresholds in the memory unit; c) determining threshold-to-threshold differences between two consecutive capture thresholds; and d) if a maximum determined threshold-to-threshold difference within the observation period is equal to or greater than a predetermined limit, adjusting a pacing output of the stimulation unit based on the maximum capture threshold determined within a first time period which is equal to or shorter than the observation period.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the United States National Phase under 35 U.S.C. §371 of PCT International Patent Application No. PCT/EP2021/050286, filedon Jan. 8, 2021, which claims the benefit of European Patent ApplicationNo. 20158056.0, filed on Feb. 18, 2020, and U.S. Provisional PatentApplication No. 62/969,179, filed on Feb. 3, 2020, the disclosures ofwhich are hereby incorporated by reference herein in their entireties.

TECHNICAL FIELD

The present invention relates to an implantable medical device accordingto the preamble of claim 1, to a method for controlling the operation ofsuch an implantable medical device according to the preamble of claim10, to a computer program product according to the preamble of claim 11and to another implantable medical device according to the preamble ofclaim 13.

BACKGROUND

Implantable medical devices for stimulating a human or animal heart,such as cardiac pacemakers, typically employ a capture control featurefor assessing ventricular capture. Capture can be described asventricular stimulation success; it is defined as ventricular cardiacactivity in response to an external or artificial stimulation (e.g., bypacemaker).

Capture control features typically use an algorithm to calculate thepacing output necessary to reliably achieve capture while limiting thepacing output to minimize power consumption of the implantable medicaldevice. The capture control feature periodically measures the capturethreshold and automatically adjusts the pacing output with the followingbasic calculation: previous threshold+safety margin=pacing output.

Often, capture control is performed once a day, wherein the appliedpacing output is decreased during a capture test to determine thecapture threshold. Starting with a pacing output having a highamplitude, the amplitude of the pacing output is iteratively decreasedto determine the lowest amplitude at which a ventricular activity stillcan be captured.

Traditional safety margin algorithms add a fixed margin to either thelast measured threshold or the maximum threshold over an evaluationperiod. These methods typically result in a comparatively higher pacingoutput and therefore require a comparatively higher io powerconsumption.

International Publication No. 2017/139197 describes a capture managementmethod by which the difference between the minimum and the maximumthreshold of a plurality of lastly determined thresholds in a rollingtime window is calculated. The higher the is determined difference, thehigher is the safety margin added to the determined capture threshold inorder to determine the pacing output to be used. Thus, this method makesuse of a variable safety margin that is added to the highest capturethreshold determined in a rolling time window, wherein the margin ishigh if the variance of the determined capture thresholds is high, andwherein the safety margin is low if the variance of the determined zocapture thresholds is low.

U.S. Publication No. 2014/0350623 describes a method to identifycandidate pulse widths corresponding to a lowest pulse energy sufficientto achieve capture within cardiac tissue of a patient. In this context,the application of different safety margins is also described.

U.S. Publication No. 2016/0346552 and U.S. Publication No. 2018/0036547exemplarily describe the application of threshold tests and theapplication of safety margins to the determined capture threshold inorder to determine the pacing output (stimulation amplitude).

The present disclosure is directed toward overcoming one or more of theabove-mentioned problems, though not necessarily limited to embodimentsthat do.

SUMMARY

It is an object of the present invention to provide an implantablemedical device for stimulating a human or animal heart, wherein thedevice has a lower power consumption than implantable devices known fromprior art but still guarantees high patient safety with respect tocardiac capture.

At least this object is achieved with an implantable medical devicehaving the features of to claim 1. Such an implantable medical device isintended for stimulating a human or animal heart. It comprises a controlunit, a memory unit, a stimulation unit for stimulating a cardiac regionof the human or animal heart, and a detection unit for detecting anelectrical signal of the same heart. In this context, the detection unittypically detects a ventricular signal of the heart. The stimulationunit may stimulate an atrium or a ventricle of the is human or animalheart. Often, the stimulation unit is intended to stimulate the rightventricle of the patient's heart.

According to the presently claimed invention, the memory unit comprisesa computer-readable program that causes the control unit to perform thesteps explained below when zo being executed on the control unit.

In a first step, capture thresholds are detected with the detectionunit. This detection is done during an observation period. In thiscontext, each capture threshold is detected in response to a sequence ofpacing pulses delivered by the stimulation unit. Thus, the detectionunit detects a cardiac activity in response to an external or artificialstimulus.

The detected capture thresholds are stored in the memory unit.Typically, a time information is stored together with the capturethresholds. Then, it can be easily seen at which time point a specificcapture threshold has been detected.

A threshold difference is determined between each pair of twoconsecutive capture thresholds. For such determination, at least twocapture thresholds are necessary. If a first capture threshold and asecond capture threshold have been detected, the threshold-to-thresholddifference between the first capture threshold and the second capturethreshold can be calculated. If afterwards a third capture threshold isdetermined, a threshold-to-threshold difference between the secondcapture threshold and the third capture threshold can be calculated. Togive an example, in case of 30 capture thresholds, 29threshold-to-threshold differences between two consecutive capturethresholds in each case will result.

The calculated threshold-to-threshold differences are then furtherevaluated. For this purpose, a maximum threshold-to-threshold differencedetermined within the observation to period is identified. If thismaximum threshold-to-threshold difference is equal to or greater than apredetermined limit, this indicates that the inter-threshold variety israther high. Then, a higher pacing output is necessary to safelyguarantee ventricular capture. Therefore, the pacing output of thestimulation unit is, in this alternative, adjusted on the basis of themaximum capture threshold determined within a first time period. In thiscontext, the first time period is equal to or shorter than theobservation period.

If, on the other hand, the maximum determined threshold-to-thresholddifference within the observation period is smaller than thepredetermined limit, this indicates that the inter-threshold variance ofthe individual thresholds is comparatively low. Then, it can also be zoguaranteed to achieve cardiac capture when only relying on the maximumamplitude from a shorter time period than the first time period.Therefore, the pacing output of the stimulation unit is, in thisalternative, adjusted on the basis of the maximum capture thresholddetermined within a second time period, wherein the second time periodis shorter than the first time period.

It should be understood that the first time period and the second timeperiod extend from the time point of adjusting the pacing output of thestimulation unit to the past. Thus, the first time period covers morecapture thresholds and therefore more threshold-to-threshold differencesthan the second time period, wherein both the first time period and thesecond time period cover the most recent threshold-to-thresholddifferences prior to the adjustment of the pacing output of thestimulation unit.

This dynamic aspect of the algorithm employed by the computer-readableprogram offers a power savings opportunity considering the power andsafety trade-off that comes with the length of the maximum thresholdevaluation period, i.e., the first time period or the second timeperiod. Lengthening the evaluation period that tracks the maximummeasured capture threshold significantly raises the residing overallaverage pace output amplitude. However, the dynamic performance lowersthe overall average pace output amplitude during periods of capturethreshold stability by shortening this maximum capture thresholdevaluation period to the second time period.

io The first time period and the second time period are rolling windowtime periods that always ends at the time at which the pacing output ofthe stimulation unit is adjusted by the method employed by thecomputer-readable program. Thus, the endpoint of the time period alwaysmoves forward in time. Likewise, the starting point of the respectivetime period also moves forward in time if the time period itself is notlengthened. Thus, the is presently claimed implantable medical device isa device that supports capture threshold processing including capturethreshold storing using a rolling window, maximum threshold measurementand threshold-to-threshold variation measurement.

In an embodiment, the implantable medical device is an intra-cardiacdevice. The device is zo capable of delivering stimulation to cardiactissue and measuring the capture threshold of cardiac capture orventricular capture, respectively.

In contrast to prior art solutions, the method employed by the presentlyclaimed implantable medical device uses a novel measure of thresholdstability to determine how long of a capture threshold evaluation periodshould be tracked to measure a patient's maximum capture threshold anddetermine the pacing output based on this maximum capture threshold.This allows a faster dynamic response during periods of stable capturethreshold which reduces overall pacing output, while maintaining safetythrough a long window during periods of capture threshold instability.

In an embodiment, the capture threshold progress is evaluated. In thisembodiment, the stored capture thresholds are, e.g., used to evaluatewhether there is a risk of an undesired disassociation of theimplantable medical device from cardiac tissue. If a continuous increaseof the capture threshold is detected, this might indicate that theimplantable medical device is about to disassociate from cardiac tissue.In such a case, immediate counteractions can be taken to guarantee safeimplantation of the implantable medical device at its intended site ofimplantation. Thus, patient safety is increased in this embodiment. Ifthe capture threshold first increases and afterwards decreases toincrease and decrease again, this can be seen as indication that thereis no disassociation of the implantable medical device from itsimplantation site, but rather reflects natural fluctuations of thecapture threshold.

In an embodiment, the step of detecting capture thresholds with thedetection unit is performed once a day. For this purpose, typically aplurality of measurements is necessary during which the pacing outputused for stimulating the cardiac tissue is lowered in an iterative way.The capture threshold is the last value of the pacing output at whichcapture can be determined, wherein the first pacing output at which nocardiac capture can be detected falls below the capture threshold.

In an embodiment, the computer-readable program causes the control unitto determine the pacing output by adding a safety margin to the maximumcapture threshold on the basis of zo which the pacing output is to beadjusted. Such a safety margin guarantees cardiac capture even if smallother variances of the capture threshold are present. Thus, such asafety margin enhances patient safety even if it consumes somewhat moreenergy than working without safety margin. Expressed in other words, thesafety margin securely ensures that cardiac capture will occur bystimulation with a pacing output that results from adding the safetymargin to the previously determined maximum capture threshold of thefirst time period or the second time period.

In an embodiment, the computer-readable program causes the control unitto set the safety margin independently on the determinedthreshold-to-threshold differences and, alternatively or additionally,independently on the determined maximum capture threshold.

Thus, in contrast to prior art solutions which rely on a variation ofthe safety margin to be applied to a specific maximum capture thresholdfor determining the final pacing output, this embodiment of thepresently claimed invention does not vary the safety margin, but ratherrelies on a skilled choice of the maximum threshold to be applied forcalculating the pacing output. As already outlined above, the presentlyclaimed approach reflects much better the physiological needs of apatient, the heart of whom is stimulated by the implantable medicaldevice, while saving at the same time a significant amount of energynecessary for pacing the patient's heart. The approach taken by thepresently described invention does not require a variable safety margin.Rather, the safety margin can be kept constant over the entire lifetimeof the implantable medical device or at least over almost the entirelifetime of the implantable medical device.

In an embodiment, the computer-readable program causes the control unitto set the safety margin during a third time period higher than afterthe third time period. In this context, the third time period is a timeperiod directly after implantation of the implantable medical device.This embodiment considers that the capture threshold is typicallysomewhat higher and more variable during the first weeks afterimplantation and then typically decreases to a lower relatively constantvalue. Thus, when combining the previous and the instant embodimentswith each other, the safety margin is varied only during the very firsttime after implantation to be then kept constant for the remaininglifetime of the implantable medical device. This can be considered as aconstant safety margin over almost the entire zo lifetime of theimplantable medical device. In an embodiment, the term “almost theentire lifetime of the implantable medical device” is to be construed asmeaning the entire lifetime minus the third time period (irrespective ofany variations of the safety margin within the third time period).

In an embodiment, the third time period is a time period covering 1 dayto 200 days, in particular 5 days to 190 days, in particular 10 days to180 days, in particular 20 days to 170 days, in particular 30 days to160 days, in particular 40 days to 150 days, in particular 50 days to140 days, in particular 60 days to 130 days, in particular 70 days to120 days, in particular 80 days to 110 days, in particular 90 days to100 days. In any case, the third time period starts immediately withimplantation of the implantable medical device, in particular withimplantation of the implantable medical device into the patient's heart.

In an embodiment, the implantable medical device is a leadlesspeacemaker. Leadless pacemakers are implanted into the patient's heart,i.e., they can also be denoted as intra-cardiac devices. Leadlesspacemakers are typically smaller than conventional pacemakers and thusoffer less space for energy sources like batteries. Therefore, the powerconsumption of leadless pacemakers is to be even better controlled thanthe power consumption of conventional pacemakers. Therefore, leadlesspacemakers are a very interesting field of application of the presentlyclaimed invention since the presently claimed invention willsignificantly extend the lifetime of leadless pacemakers and can thusmake such devices even more attractive than they already are.

In an embodiment, the computer-readable program causes the control unitto decrease the voltage of the pacing output at most by a predeterminedmaximum value each day. If this embodiment is applied, an initialvoltage of the pacing output is more limited than potentially possibleaccording to the determined capture thresholds and threshold-to-isthreshold differences. Therefore, an operation of the implantablemedical device by this embodiment results in a higher energy consumptionthan absolutely necessary. However, it further increases patient safety.Furthermore, the predetermined maximum value by which the voltage of thepacing output can be at most decreased each day can be set such that thetime period during which the energy consumption of the implantablemedical device is zo higher than necessarily needed is limited to a fewdays or a few weeks. In doing so, it is possible to set the pacingoutput to a higher level in an initial time period of operation of theimplantable medical device, e.g., directly after implantation. To give afurther example, the limited decrease of the voltage of the pacingoutput can be employed during the third period of time. Then, asufficiently high pacing output to achieve cardiac capture can beguaranteed even though the cardiac tissue of the patient might not haveyet achieved its final susceptibility with respect to a stimulation by apacing pulse.

In an embodiment, the predetermined maximum value of the step down sizelies in a range between 0.05 V and 0.2 V, in particular between 0.075 Vand 0.15 V, in particular between 0.1 V and 0.12 V.

In an embodiment, the observation period and/or the first time periodare a time period covering 7 days to 50 days, in particular 10 days to45 days, in particular 15 days to 40 days, in particular 20 days to 35days, in particular 25 days to 30 days. In an embodiment, the first timeperiod has the same length as the observation period, i.e., the firsttime period equals the observation period. To give an example, theobservation period might cover 30 days. Then, the first time periodwould cover the last 30 days prior to the day on which the pacing outputof the stimulation unit is adjusted according to the method employed bythe presently claimed implantable medical device.

In an embodiment, the second time period is a time period covering 2days to 14 days, in particular 3 days to 13 days, in particular 4 daysto 12 days, in particular 5 days to 11 days, in particular 6 days to 10days, in particular 7 days to 9 days. A particular appropriate secondtime period is a time period of 2 days to 6 days, e.g., 3 days, 4 days,5 days or 6 days.

An aspect of the present invention relates to a method for controllingthe operation of an implantable medical device for stimulating a humanor animal heart according to the preceding explanations. This methodcomprises the steps explained in the following.

zo First, an electrical signal of a human or animal heart is detectedwith a detection unit. This detection serves for detecting capturethresholds during an observation period. Each capture threshold isdetected in response to a sequence of pacing pulses delivered by astimulation unit for stimulating a cardiac region of the same heart.

The detected capture thresholds are stored in the memory unit of theimplantable medical device.

Furthermore, threshold-to-threshold differences between two consecutivecapture thresholds in each case are determined.

Afterwards, it is decided if a maximum determined threshold-to-thresholddifference within the observation time period is equal to or greaterthan a predetermined limit (first alternative) or lower than thepredetermined limit (second alternative). In case of the firstalternative, a pacing output of the stimulation unit is adjusted on thebasis of the maximum capture threshold determined within a first timeperiod. In this context, the first time period is equal to or shorterthan the observation period. In case of the second alternative, thepacing output of the stimulation unit is adjusted on the basis of themaximum capture threshold determined within a second time period. Inthis context, the second time period is shorter than the first timeperiod. The first time period and the second time period are timeperiods reaching from the time point of adjusting the pacing output ofthe stimulation unit to the past.

An aspect of the present invention relates to a computer program productcomprising computer-readable code that causes a control unit to performthe following steps when executed on the control unit.

First, an electrical signal of a human or animal heart is detected witha detection unit. This detection serves for detecting capture thresholdsduring an observation period. Each capture threshold is detected inresponse to a sequence of pacing pulses delivered by a stimulation unitfor stimulating a cardiac region of the same heart.

zo The detected capture thresholds are stored in the memory unit of animplantable medical device.

Furthermore, threshold-to-threshold differences between two consecutivecapture thresholds in each case are determined.

Afterwards, it is decided if a maximum determined threshold-to-thresholddifference within the observation time period is equal to or greaterthan a predetermined limit (first alternative) or lower than thepredetermined limit (second alternative). In case of the firstalternative, a pacing output of the stimulation unit is adjusted on thebasis of the maximum capture threshold determined within a first timeperiod. In this context, the first time period is equal to or shorterthan the observation period. In case of the second alternative, thepacing output of the stimulation unit is adjusted on the basis of themaximum capture threshold determined within a second time period. Inthis context, the second time period is shorter than the first timeperiod. The first time period and the second time period are timeperiods reaching from the time point of adjusting the pacing output ofthe stimulation unit to the past.

An aspect of the present invention relates to a medical method oftreatment of a human or animal patient in need of such treatment. Thistreatment takes place by means of an implantable medical device forstimulating a human or animal heart, in particular with an implantablemedical device according to the preceding explanations. Such animplantable medical device comprises a control unit, a memory unit, astimulation unit for stimulating a cardiac region of a human or animalheart and a detection unit for detecting an electrical signal of thesame heart. The method comprises the steps explained in the following.

First, an electrical signal of a human or animal heart is detected withthe detection unit. This detection serves for detecting capturethresholds during an observation period. Each capture threshold isdetected in response to a sequence of pacing pulses delivered by thestimulation unit for stimulating a cardiac region of the same heart.

The detected capture thresholds are stored in the memory unit of theimplantable medical device.

Furthermore, threshold-to-threshold differences between two consecutivecapture thresholds in each case are determined.

Afterwards, it is decided if a maximum determined threshold-to-thresholddifference within the observation time period is equal to or greaterthan a predetermined limit (first alternative) or lower than thepredetermined limit (second alternative). In case of the firstalternative, a pacing output of the stimulation unit is adjusted on thebasis of the maximum capture threshold determined within a first timeperiod. In this context, the first time period is equal to or shorterthan the observation period. In case of the second alternative, thepacing output of the stimulation unit is adjusted on the basis of themaximum capture threshold determined within a second time period. Inthis context, the second time period is shorter than the first timeperiod. The first time period and the second time period are timeperiods reaching from the time point of adjusting the pacing output ofthe stimulation unit to the past.

Afterwards, the human or animal heart is stimulated by applying a pacingpulse by the stimulation unit with the pacing output adjusted in thepreceding step. Thus, the pacing pulse can have different amplitudesdepending on the previously observed variance of the capture threshold.Typically, the pacing pulse has a higher amplitude (i.e., thestimulation unit is operated with a higher pacing output) if thevariance of the detected threshold-to-threshold differences wascomparatively high. In contrast, the pacing pulse will have a loweramplitude (i.e., the stimulation unit is operated with a lower pacingoutput) in case that lower variances between the individual capturethresholds have been determined, i.e., if the threshold-to-thresholddifferences were comparatively lower.

A further aspect of the present invention is another implantable medicaldevice for stimulating human or animal heart that can be combined withany of the preceding explained embodiments but that is also claimedindependent on the preceding explained aspects and embodiments. Thisfurther implantable medical device comprises a control unit, a memoryunit, a stimulation unit for stimulating a cardiac region of a human oranimal heart, and a detection unit for detecting an electrical signal ofthe same heart.

The memory unit comprises a computer-readable program that causes thecontrol unit to perform the steps explained in the following whenexecuted on the control unit.

First, capture thresholds are detected with the detection unit during anobservation period.

In this context, each capture threshold is detected in response to asequence of pacing pulses delivered by the stimulation unit.

The detected capture thresholds are stored in the memory unit.

A voltage of the pacing output of the stimulation unit is decreased atmost by a predetermined maximum value each day. In this context, thevoltage of the pacing output remains at least as high as a maximumcapture threshold determined within a time period being equal to orshorter than the observation period. According to an embodiment, thevoltage of the pacing output remains at least as high as a maximumcapture threshold determined within a time period being equal to orshorter than the observation period with an added safety margin. Indoing so, it is guaranteed that the applied voltage of the pacing outputis always at least as high as the determined capture threshold with anadded safety margin, but at the same time is reduced only in small stepsfrom the previous value. This helps to address sudden decreases incapture threshold that may only be temporary. According to an embodimentof the present invention, there is a predetermined value defined whichrepresents the maximum value for a variation of the pacing output,especially for one decrease of the pacing output.

In an embodiment, the limited decrease of the voltage of the pacingoutput is performed only over a predetermined period of time, e.g.,during the third time period as defined above.

In an embodiment, the predetermined maximum value lies in a rangebetween 0.05 V and 0.2 V, in particular between 0.075 V and 0.15 V, inparticular between 0.1 V and 0.12 V.

In an embodiment, the implantable medical device does not only implementa limited decrease of the initial voltage of the pacing output, but alsoan adjustment of the pacing output in response to observed capturethreshold variances. In this embodiment, the computer-readable programcauses the control unit to adjust the pacing output of the stimulationunit either according to a first alternative or according to a secondalternative. According to the first alternative, the pacing output isadjusted on the basis of the maximum capture threshold determined withina first time period, if a maximum determined threshold-to-thresholddifference within the observation period is equal to or greater than apredetermined limit. In this context, the first time period is equal toor shorter than the observation period. According to the secondalternative, the pacing output of the stimulation unit is adjusted onthe basis of the maximum capture threshold determined within a secondtime period, if the maximum determined threshold-to-threshold differencewithin the observation period is smaller than the predetermined limit.In this context, the second time period is shorter than the first timeperiod.

Thus, in this embodiment, the voltage of the pacing output is decreasedeach day by the predetermined maximum value until it reaches the outputof the algorithm evaluating the capture threshold variances in the past.Instances of non-capture are reliably avoided by this operational mode.If, however, the output of the algorithm evaluating the capturethreshold variances in the past results in a higher necessary capturethreshold than the voltage of the last pacing output minus the maximumvalue by which the voltage of the pacing output has been decreased sofar at most each day, the pacing output is immediately updated to thepacing output determined on the basis of the maximum capture thresholddetermined by the algorithm.

An aspect of the present invention relates to a method for controllingthe operation of an implantable medical device for stimulating a humanor animal heart, the method comprising the following steps: a)detecting, with a detection unit for detecting an electrical signal of ahuman or animal heart, capture thresholds during an observation period,each capture threshold being detected in response to at least one pacingpulse or a sequence of pacing pulses delivered by a stimulation unit forstimulating a cardiac region of the same heart; b) storing the detectedcapture thresholds in a memory unit of the implantable medical device;c) decreasing a voltage of a pacing output of the stimulation unit atmost by a predetermined maximum value each day, wherein the voltage ofthe pacing output remains at least as high as a maximum capturethreshold determined within a time period being equal to or shorter thanthe observation period. According to an embodiment, the voltage of thepacing output remains at least as high as a maximum capture thresholddetermined within a time period being equal to or shorter than theobservation period with an added safety margin.

An aspect of the present invention relates to a computer program productcomprising computer-readable code that causes a control unit to performthe following steps when executed on the control unit: a) detecting,with a detection unit of an implantable medical device for stimulating ahuman or animal heart, the detection unit being configured to detect anelectrical signal of a human or animal heart, capture thresholds duringan observation period, each capture threshold being detected in responseto a pacing pulse delivered by a stimulation unit of the implantablemedical device, the stimulation unit being configured to stimulate acardiac region of the same heart; b) storing the detected capturethresholds in a memory unit of the implantable medical device; c)decreasing a voltage of a pacing output of the stimulation unit at mostby a predetermined maximum value each day, wherein the voltage of thepacing output remains at least as high as a maximum capture thresholddetermined within a time period being equal to or shorter than theobservation period. According to an embodiment, the voltage of thepacing output remains at least as high as a maximum capture thresholddetermined within a time period being equal to or shorter than theobservation period with an added safety margin.

An aspect of the present invention relates to a method of treatment of ahuman or animal patient in need of such treatment by means of animplantable medical device for stimulating a human or animal heart,wherein the implantable medical device comprises a control unit, amemory unit, a stimulation unit for stimulating a cardiac region of ahuman or animal heart, and a detection unit for detecting an electricalsignal of the same heart, the method comprising the following steps: a)detecting, with the detection unit, capture thresholds during anobservation period, each capture threshold being detected in response zoto a pacing pulse de-livered by the stimulation unit; b) storing thedetected capture thresholds in the memory unit; c) decreasing a voltageof a pacing output of the stimulation unit at most by a predeterminedmaximum value each day, wherein the voltage of the pacing output remainsat least as high as a maximum capture threshold determined within a timeperiod being equal to or shorter than the observation period with anadded safety margin; d) stimulating the human or animal heart byapplying a pacing pulse with the pacing output adjusted in the precedingstep.

All embodiments of the individual implantable medical devices describedherein can be combined in any desired way and can be transferred to therespective other implantable medical device, to the described methodsand to the described computer program products.

Furthermore, any embodiments of the described methods can be combined inany desired way and can be transferred to the respective other methods,to the different implantable medical devices and to the computer programproducts. Finally, any embodiments of the computer program products canbe combined in any desired way and can be transferred in any combinationto the respective other computer program products, to the describedimplantable medical devices, and to the described methods.

Additional features, aspects, objects, advantages, and possibleapplications of the present disclosure will become apparent from a studyof the exemplary embodiments and examples described below, incombination with the Figures and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details of aspects of the present invention will be explainedwith respect to exemplary embodiments and accompanying Figures. In theFigures:

FIG. 1 shows a schematic workflow of a first embodiment of a method fordetermining a pacing output of a stimulation unit of an implantablemedical device;

FIG. 2 shows a schematic workflow of a second embodiment of a method fordetermining a pacing output of a stimulation unit of an implantablemedical device;

FIG. 3 shows a schematic representation of an implantable medical deviceof a first embodiment; and

FIG. 4 shows a schematic representation of an implantable medical deviceof a second embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates the workflow of a method implemented by a cardiacpacemaker as implantable medical device. First, a detection unit of thecardiac pacemaker serves for detecting 110 capture thresholds during anobservation period. Afterwards, a determination 120 ofthreshold-to-threshold differences between two consecutive capturethresholds is carried out.

Then, a decision 130 takes place whether the maximumthreshold-to-threshold difference determined within the observationperiod is either equal to or above a preset limit or below this limit.Thereby, the limit is set to be 0.4 V in the embodiment of FIG. 1 . Ifthe maximum determined threshold-to-threshold difference is at least 0.4V, a selection 140 of the maximum capture threshold during the past 30days takes place. In this context, 30 days serve as first time period.If, on the other hand, the maximum determined threshold-to-thresholddifference is below 0.4 V, a selection 150 of the maximum determinedcapture threshold during the past 3 days takes place. In this context, 3days serve as second time period. Afterwards, an addition 160 of asafety margin to the selected maximum capture threshold is carried out.

Finally, an adjustment 170 of a pacing output for a pacing pulse by astimulation unit of the implantable medical device is performed. Thisadjustment is based on the selected maximum capture threshold anddefines the pacing output to be the sum of the selected capturethreshold and the safety margin.

This method is typically applied once a day by the cardiac pacemaker.

The safety margin added to the selected maximum capture threshold instep 160 is chosen to be 0.4 V in case that the cardiac pacemaker hasbeen implanted no longer than a predefined period since implant and isreduced to 0.3 V in case that the implantation of the cardiac pacemakerhas been carried out longer than the predefined time period. Accordingto an embodiment, the predefined period is 20 to 150 days, or 50 to 120days, or 70 to 120 days, or 90 to 120 days, or 100 to 120 days, or 112days.

FIG. 2 shows a schematic workflow of a further method that is applied byanother cardiac pacemaker, serving as further embodiment of animplantable medical device.

First, a determination 210 of capture thresholds takes place during anobservation period. This detection is carried out with a detection unitof the cardiac pacemaker. Each capture threshold is determined inresponse to a sequence of pacing pulses delivered by a stimulation unitof the cardiac pacemaker.

The capture thresholds generally serve for adjusting a pacing output ofthe cardiac pacemaker. However, prior to adjusting the pacing output, adetermination 220 takes place regarding a decrease of the previouslyapplied pacing output. If a voltage U of the previously applied pacingoutput reduced by 0.1 V is at least as high as the determined capturethreshold CT (optionally plus a safety margin), an adjustment 230 of thepacing output to the previously applied pacing output minus 0.1 V takesplace.

If, however, the determination 220 gives the result that the detection210 of the capture threshold (optionally plus a safety margin) resultedin a higher capture threshold CT than a voltage U of the previouslyapplied pacing output reduced by 0.1 V, an adjustment 240 of the pacingoutput on the basis of the determined capture threshold takes place (asafety margin is optionally considered and added to the detected maximumcapture threshold). According to an embodiment, the pacing output isimmediately increased to the output determined by the algorithm.

This method guarantees that the pacing output is reduced in an iterativeway by a maximum value which is set to 0.1 V in the present embodimentuntil the pacing output reaches the algorithm-determined pacing output.This method is performed such that an unforeseeable increase in thenecessary capture threshold will automatically lead to an increase ofthe pacing output so that the safe cardiac capture can always beguaranteed.

Furthermore, even if no iterative decrease of a previous pacing outputis done, the method guarantees that the applied pacing output neverfalls below the necessary capture threshold.

The embodiment shown in FIG. 2 can be combined with the embodiment ofFIG. 1 or can be implemented without the embodiment of FIG. 1 in acardiac pacemaker.

FIG. 3 shows a schematic representation of an implantable medical device1 (e.g., a cardiac pacemaker) for stimulating a human or animal heart H,comprising a control unit 10 (e.g., a processor), a memory unit 12, astimulation unit 14 for stimulating a cardiac region of a human oranimal heart, and a detection unit 16 for detecting an electrical signalof the same heart H. The memory unit 12 comprises a computer-readableprogram that causes the control unit 10 to perform the steps of theworkflow shown in FIG. 1 when executed on the control unit 10.

FIG. 4 shows a schematic representation of an implantable medical device1′ (e.g., a cardiac pacemaker) for stimulating a human or animal heartH′, comprising a control unit 10′ (e.g., a processor), a memory unit12′, a stimulation unit 14′ for stimulating a cardiac region of a humanor animal heart H′, and a detection unit 16′ for detecting an electricalsignal of the same heart H′. The memory unit 12′ comprises acomputer-readable program that causes the control unit 10′ to performthe steps of the workflow shown in FIG. 2 when executed on the controlunit 10′

It will be apparent to those skilled in the art that numerousmodifications and variations of the described examples and embodimentsare possible in light of the above teachings of the disclosure. Thedisclosed examples and embodiments are presented for purposes of zoillustration only. Other alternate embodiments may include some or allof the features disclosed herein. Therefore, it is the intent to coverall such modifications and alternate embodiments as may come within thetrue scope of this invention, which is to be given the full breadththereof. Additionally, the disclosure of a range of values is adisclosure of every numerical value within that range, including the endpoints.

1. Implantable medical device for stimulating a human or animal heart,comprising a control unit, a memory unit, a stimulation unit forstimulating a cardiac region of a human or animal heart, and a detectionunit for detecting an electrical signal of the same heart, wherein thememory unit comprises a computer-readable program that causes thecontrol unit to perform the following steps when executed on the controlunit: a) detecting, with the detection unit, capture thresholds duringan observation period, each capture threshold being detected in responseto a sequence of pacing pulses delivered by the stimulation unit; b)storing the detected capture thresholds in the memory unit; c)determining threshold-to-threshold differences between two consecutivecapture thresholds in each case; and d) if a maximum determinedthreshold-to-threshold difference within the observation period is equalto or greater than a predetermined limit, adjusting a pacing output ofthe stimulation unit on the basis of the maximum capture thresholddetermined within a first time period, the first time period being equalto or shorter than the observation period; or if the maximum determinedthreshold-to-threshold difference within the observation period issmaller than the predetermined limit, adjusting the pacing output of thestimulation unit on the basis of the maximum capture thresholddetermined within a second time period, the second time period beingshorter than the first time period.
 2. Implantable medical deviceaccording to claim 1, wherein the computer-readable program causes thecontrol unit to determine the pacing output by adding a safety margin tothe maximum capture threshold on the basis of which the pacing output isadjusted.
 3. Implantable medical device according to claim 2, whereinthe computer-readable program causes the control unit to set the safetymargin independently on the determined threshold-to-thresholddifferences.
 4. Implantable medical device according to claim 2, whereinthe computer-readable program causes the control unit to set the safetymargin during a third time period greater than after the third timeperiod, the third time period being a time period starting withimplantation of the implantable medical device.
 5. Implantable medicaldevice according to claim 1, wherein the implantable medical device is aleadless pacemaker.
 6. Implantable medical device according to claim 1,wherein the computer-readable program causes the control unit todecrease a voltage of the pacing output at most by a predeterminedmaximum value each day.
 7. Implantable medical device according to claim6, wherein the predetermined maximum value lies in a range between 0.05V and 0.2 V.
 8. Implantable medical device according to claim 1, whereinthe observation period and/or the first time period are a time periodcovering 7 days to 50 days.
 9. Implantable medical device according toclaim 1, wherein the second time period is a time period covering 2 daysto 14 days.
 10. (canceled)
 11. Computer program product comprisingcomputer-readable code that causes a control unit to perform thefollowing steps when executed on the control unit: a) detecting, with adetection unit of an implantable medical device for stimulating a humanor animal heart, the detection unit being configured to detect anelectrical signal of a human or animal heart, capture thresholds duringan observation period, each capture threshold being detected in responseto a pacing pulse delivered by a stimulation unit of the implantablemedical device, the stimulation unit being configured to stimulate acardiac region of the same heart; b) storing the detected capturethresholds in a memory unit of the implantable medical device; c)determining threshold-to-threshold differences between two consecutivethresholds in each case; and d) if a maximum determinedthreshold-to-threshold difference within the observation period is equalto or greater than a predetermined limit, adjusting a pacing output ofthe stimulation unit on the basis of the maximum capture thresholddetermined within a first time period, the first time period being equalto or shorter than the observation period; or if the maximum determinedthreshold-to-threshold difference within the observation period issmaller than the predetermined limit, adjusting the pacing output of thestimulation unit on the basis of the maximum capture thresholddetermined within a second time period, the second time period beingshorter than the first time period.
 12. (canceled) .
 13. Implantablemedical device for stimulating a human or animal heart, comprising acontrol unit, a memory unit, a stimulation unit for stimulating acardiac region of a human or animal heart, and a detection unit fordetecting an electrical signal of the same heart, wherein the memoryunit comprises a computer-readable program that causes the control unitto perform the following steps when executed on the control unit: a)detecting, with the detection unit, capture thresholds during anobservation period, each capture threshold being detected in response toa pacing pulse delivered by the stimulation unit; b) storing thedetected capture thresholds in the memory unit; c) decreasing a voltage(U) of a pacing output of the stimulation unit at most by apredetermined maximum value each day, wherein the voltage (U) of thepacing output remains at least as high as a maximum capture thresholddetermined within a time period being equal to or shorter than theobservation period.
 14. Implantable medical device according to claim13, wherein the predetermined maximum value lies in a range between 0.05V and 0.2 V.
 15. Implantable medical device according to claim 13,wherein the computer-readable program causes the control unit to i)adjust the pacing output of the stimulation unit on the basis of themaximum capture threshold determined within a first time period, if amaximum determined threshold-to-threshold difference within theobservation period is equal to or greater than a predetermined limit,the first time period being equal to or shorter than the observationperiod; or ii) adjust the pacing output of the stimulation unit on thebasis of the maximum capture threshold determined within a second timeperiod, if the maximum determined threshold-to-threshold differencewithin the observation period is smaller than the predetermined limit,the second time period being shorter than the first time period.